Service

What is the throttle body and how does it work?

The throttle body is an air metering device mounted between the air filter and snorkel, and the intake plenum. Within the throttle body is a movable throttle plate whose position controls the amount of air that enters the engine to determine engine speed. Throttle body designs vary. Some incorporate an idle air control valve, throttle position sensor, and other electronic throttle controls. The throttle plate in the throttle body can be controlled directly by an accelerator pedal cable or fully electronically in the newest drive-by-wire systems.

When to consider replacing the throttle body:

Check engine light and/or reduced power warning light is on. Most modern throttle bodies have electrical components, such as a throttle position sensor. These components are monitored by the powertrain control module (PCM). If the check engine light or reduced power warning light comes on, a mechanic will determine if any of the stored trouble codes implicate a throttle body malfunction.

Wrong idle speed. Carbon deposits in the throttle body, particularly around the movable throttle plate or in the idle air control valve, can cause the engine idle speed to be too low or too high.

Poor transmission shifting. In some applications, transmission shift timing relies on signal outputs from the throttle body. If the throttle position sensor is defective, that might adversely affect shift timing and feel.

How do mechanics replace the throttle body?

The engine cover is removed, if necessary.

The flexible rubber snorkel from the air filter housing to the throttle body is disconnected. Typically, the connection is made with a large stainless steel hose clamp.

The electrical connections to the throttle body are removed.

If the throttle body is not a drive-by-wire system, the accelerator cable and cruise control cable are disconnected and set aside.

The bolts retaining the throttle body to the plenum, the gasket, and the throttle body are removed. If the throttle body is being cleaned and tested for re-use, approved chemicals are used in the cleaning process.

The new or serviced throttle body is re-attached to the plenum and the bolts torqued to factory specifications.

All cables and electrical connections are restored. The intake air snorkel is reconnected.

If applicable, the electronic throttle installation and idle re-learn procedures are performed using an appropriate scan tool.

Finally, the engine is started, brought to normal operating temperature, and idle speed is checked. The car is road tested to ensure normal operation and no illumination of warning or service lights.

Is it safe to drive with a throttle body problem?

Yes. But, the vehicle may be limited in power or put into what is referred to as limp mode, in order to get the vehicle to a repair facility. If the check engine light is on, or the electronic throttle control warning light is on, but there is no noticeable difference in engine performance, the car can be safely driven. However, it is best to have it diagnosed and repaired at your earliest convenience to avoid unexpected breakdown or possible damage to the catalytic converter.

When replacing the throttle body keep in mind:

Many modern throttle bodies have spring loaded sensors and plastic gears that are not intended to be manipulated directly during any diagnostics or inspections. These components are controlled electronically or generate signals. It is best to let a mechanic use approved tests to diagnose the problem.

Wiring faults, bad grounds, or bad terminal connections can make it appear as though an electronically controlled throttle has failed. A mechanic will always rule out all other causes before replacing the throttle body.

When cleaning the throttle body, special care should be taken to use only special spray cleaners designed to not damage electrical components or sensors.